COMP 421 /CMPET 401

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COMP 421 /CMPET 401

• COMMUNICATIONS and NETWORKING
• CLASS 2

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OSI Reference Model

• Developed by the International Standards
  Organization (ISO) to facilitate the
  international standardization of communications
  protocols
• For U.S. ANSI (American National Standard
  Institute) - www.ansi.org
• OSI is ISO's Basic Reference Model for Open
  Systems Interconnect (hence ISO/OSI)
• The Reference Model itself is not a Network
  Architecture (does not specify any protocols or
  services)

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The ISO/OSI Reference Model

• The model describes computer communications
  protocols in a general sense to facilitate
  discussion
• No assumptions are made regarding
• Programming language bindings
• Operating system bindings
• Applications programming interfaces
• Development of the model started in the
  mid-1970s
• Biggest Problems
• Very long time to complete the model and protocol
  standards
• Very hard to understand the detailed standards
• Difficult (expensive) to get the standards
  documents

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OSI MODEL
5
OSI MODEL
The seven layers divided into two important
subnets 1. Communications Subnet This is
comprised of the lower 3 layers 2. Host Process
This is comprised of the upper three layer The
network layer is middle layer and the first end
to end layer. It acts as buffer between the two
subsets.
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ISO/OSI Reference Model - Why 7 Layers

• One layer for each level of abstraction
• Each layer performs (ideally) a limited, well
  defined function
• Functions for each layer are selected with
  International Standardization as a goal
• Layer boundaries are chosen to minimize
  information crossing the interface
• Want to keep the model manageable (5 would have
  been nice) but not have to jumble together
  distinct functions

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OSI Model
App Process X
App Process Y
Application Data
Application Data
AH
Data Unit
PH
Data Unit
SH
Data Unit
TH
Data Unit
NH
Data Unit
F A C
FCS F
BITS
Physical Transmission Medium
Communication Path
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OSI Layer 1
Layer 1 is the Physical Layer. It handles bit
transmission between one node and the next. The
functions of this layer include interfacing with
the transmission media, encoding the data signal,
defining the range of the voltage or current
magnitudes, defining the connector sizes, shape,
and anything generally associated with the
physical transmission of a bit stream.
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OSI Layer 1 - Physical layer

• Primary function is transmitting raw bits over a
  physical communications channel
• Primary design issues include mechanical,
  electrical, functional, procedural
  characteristics
• what voltage represents a 1 versus a 0
• How many pins in and the shell shape the
  connector.
• Defines functions between the system and
  transmission medium
• Specifies sequence of events by which bits
  streams are exchanged across the physical medium
• By raw bits we mean there is no interpretation
  of the bits - stream of bits in and bits out

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OSI Layer 2 - Data Link layer

• Primary function is to make Layer 1 into what
  appears to be a channel free of undetected errors
• Deals with data in chunks (typically 100s-1000s
  of bytes) generally called Frames
• This layer must create/recognize frame boundaries
• remember - Physical layer does not care
• often requires special bit patterns to signal
  boundaries
• may have to deal with possibility of pattern
  appearing in data

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OSI Layer 2
In other words it maintains the reliable
communications link between adjacent nodes. The
DLL inserts addresses in the data frame and
provides error control for the data.
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OSI Layer 2 - Data Link layer

• Among the key issues dealt with are
• Error handling (e.g. corrupted frame)
• Flow control
• Providing various qualities of service
• For Broadcast networks, a key issue is
  controlling access to the channel
• Use a sub-layer called the Media Access Control
  (MAC) sub-layer

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OSI Layer 3 - Network layer

• Primary function is to control the operation of
  the layers below
• Among the key issues dealt with are
• Routing packets from source to destination
  through the network (or multiple networks) using
  static or dynamic routing algorithms
• Controlling congestion in the network
• Accounting functions (for billing)
• Translating between protocols across
  heterogeneous networks
• Concerned with Addressing

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OSI Layer 3
This layer establishes the path for the traveling
data packet
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OSI Layer 4 - Transport layer

• First end-to-end layer
• Uses the network to (most often) provide higher
  layers with a connection oriented, reliable,
  error free channel that delivers messages (or
  byte stream) in order
• Layer 4 of the OSI Model coordinates
  communications between systems.
• May also perform flow control
• Often performs multiplexing of multiple transport
  connections over one or more network connections
• Generally requires Address (or naming)

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OSI Layer 4
This layer provides reliable delivery of host
messages originating at layer 7 the same way as
the DLL assures reliable delivery of frames
between adjacent nodes. This is the layer
responsible for Segmenting long messages in
smaller units (packets) and then Reassembling
them at the other end.
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OSI Layer 5 - Session layer

• Manages dialog control (e.g. may manage whos
  turn it is to talk in a high-level half-duplex
  protocol)
• Manages synchronization of transactions which may
  need to be able to roll back in case of a crash
• Sort of an unwanted layer, this layer is usually
  very thin and little more than a pass through for
  most protocols
• Key services provided include
• Dialogue discipline
• Grouping - data mark as belonging to a special
  group
• Recovery checkpoint mechanism

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OSI Layer 5
In other words it establishes and terminates
process to process communications Sessions
between hosts.
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OSI Layer 6 - Presentation layer

• Rather than being concerned with moving
  information, the Presentation layer is concerned
  with the interpretation of information
  representation
• Ensures that the syntax and meaning is the same
  for each participant in a communication
• Provides for standard representation and may
  provide capabilities for conversion of data

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OSI Layer 6
Simply put this layer establishes the syntax in
which data is exchanged between the two hosts.
It provides a data manipulation function rather
than a communication function (data
compression and data encryption are examples of
this layers activities)
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OSI Layer 7 - Application layer

• The layer where end-user applications live
• This is the highest level of abstraction and the
  level which is of primary importance (for most
  users)
• All the rest of the layers exist to support these
  applications
• Layering exists so we can move these around to
  different machines, and so they can communicate
  across any platforms - Open Systems Interconnect

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OSI Layer 7
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OSI Examples
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Review - Functions of the OSI Layers

• Layer 1 (physical) Transmission of bits
• Layer 2 (data link) Transmission of frames on
  one given link
• Layer 3 (network) Routing of packets through the
  network
• Layer 4 (transport) End-to-end delivery of
  messages

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Review - Functions of the OSI Layers

• Layer 5 (session) Setup and management of
  end-to-end conversation, synchronization
• Layer 6 (presentation) Formatting, encryption,
  and compression of data
• Layer 7 (application) user applications

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Introduction to TCP/IP
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What is TCP/IP

• Transmission Control Protocol/Internet Protocol
• TCP/IP refers to an entire suite of networking
  protocols, developed for use on the Internet
• TCP and IP are certainly two of the most important

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TCP/IP Protocol Suite

• Advanced Research Project Agency (ARPA) of DoD
  sponsored the development of ARPANET in 1970s.
• TCP/IP has been adopted as the ARPANET protocol
  suite
• TCP/IP became popular by the inclusion of this
  protocol in BSD Unix system (a version of Unix
  developed by University of California _at_ Berkley)

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TCP/IP (cont.)

• Transport Layer-TCP (Transmission Control
  Protocol)
• Provides fully reliable, connection-oriented
  service
• Byte-stream transmission
• Network Layer- IP (Internet Protocol)
• IP provides datagram service (used in packet
  switching)
• It is connectionless unreliable service
• IP handles routing

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TCP/IP Characteristics

• TCP/IP provides the services necessary to
  interconnect computers and to interconnect
  networks, creating the Internet
• Independence from underlying network topology,
  physical network hardware, and OS
• Unique IP Address
• Universal connectivity throughout the network
• Standardize high-level protocols

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TCP/IP Protocol Architecture Model
Application
Application
TCP
TCP
IP
IP
Network Access
Network Access
Network
Physical
Physical
Trans- Mission System
Source
Transmitter
Receiver
Destination
Source System
Destination System
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A Comparison
Application
User Space
Application
Presentation

Session
Software
Transport

Transport
Network
IP
Operating System
Network Access
Firmware
Data Link

Hardware
Physical
Physical
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TCP/IP Network Structure
UDP User Datagram Protocol ICMP Internet
Control Message Protocol IP
Internet Protocol ARP Address Resolution
Protocol RARP Reverse ARP
OSI Layer 5-7
OSI Layer 4
OSI Layer 3
ARP
RARP
ICMP
OSI Layer 1-2
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Port Number
XNS protocol suite
TCP/IP protocol suite
Ethernet cable 1
Ethernet cable 2
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Port Assignments

• Servers are known by ports number
• FTP 20, TELNET 23, SMTP 25, HTTP 80
• Port numbers are generally allocated by
• 0 --not used
• 1-255 --Reserved ports for well-known services
• 256-1023 --Other reserved ports
• 1024-65535 --user-defined server ports
• Unix stores general used ports in /etc/services
  directory

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Hierarchical Addressing Scheme

• Connection defines the communication link between
  two processes

UDP User Datagram Protocol
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TCP/IP Internetworking
Router
Token Ring
Private Nets and Internet
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LAN and Devices
LANs are designed to

• Operate within a limited geographic area
• Allow multi-access to high-bandwidth media
• Control the network privately under local
  administration
• Provide full-time connectivity to local services
• Connect physically adjacent devices

ATM Switch
Ethernet Switch
Bridge
Hub
Router
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Wide-Area Networks and Devices
WANs are designed to

• Operate over geography of telecommunications
  carriers
• Allow access over serial interfaces operating at
  lower speeds
• Control the network subject to regulated public
  services
• Provide full-time and part-time connectivity
• Connect devices separated over wide, even global
  areas

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TCP/IP Architectural Layers
Application
Network Applications
End-to-end Services
Transport
Internet
Routing
Network
Network Interface
Physical
Transmission
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Layer Hardware
Application
Transport
Internet

• Routers, PADs, X.25 switches
• Bridges, LAN switches, ATM switches and terminal
  servers
• Transceivers, repeaters, hubs, FDDI
  concentrators, modems, terminal adapters, DSUs,
  CSUs, MUX and NICs

Network
Physical
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Transceivers

• A transceiver connects a network device to the
  network cable
• A transceiver listens to the bus to determine if
  it is being used by another station
• A transceiver determines if the bus is being used
  by another station
• A transceiver alerts the connected device when
  there is a collision during transmission
• A transceiver may have DIP switches for
  controlling the exchange of SQE or heartbeat
  signals with the directly connected device.

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Transceivers
Attachment Interface Unit (AUI) The portion of
the Ethernet standard that specifies how a cable
is to be connected to an Ethernet card. AUI
specifies a coaxial cable connected to a
transceiver that plugs into a 15-pin socket on
the network interface card (NIC).
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Repeaters

• A repeater is used to connect two segments of the
  same network
• A repeater receives a signal from one segment,
  cleans and boosts the signal and sends it to the
  other segment
• A repeater is responsible for ensuring that a
  collision is propagated to all attached segments
• A repeater may be used to extend the network
  beyond the limitations of the networks
  architecture by increasing segment length
• Cannot add an infinite number of repeaters as
  this would adversely affect collision propagation.

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Hubs

• A hub often attaches at least four nodes and many
  hubs include connectors for linking to other hubs
• A hub provides connectivity by passing incoming
  signals to connected nodes
• Hubs may be cascaded together to allow small
  workgroups with low-intensity applications to be
  formed
• Hubs typically have LEDs to indicate the status
  of each port
• Hubs may do partitioning to allow isolation of a
  non-functioning node
• Hubs allow connection to different physical media.

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NICs

• A NIC is an internetworking device that is a
  component part of a much larger host
• NICs are used to connect the systems to the
  network
• NICs will be different for each type of host
  system and type of network topology (and for each
  bus type)
• Remote access is achieved through remote access
  to the host system
• When installing a NIC it is important to consider
  the network topology, cabling and electrical
  considerations to avoid network disruption.

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TCP/IP Networking Software

• TCP/IP protocol suites define a set of universal
  communication services
• Services can be implemented in a standardized
  manner in the networking software, normally
  bundled with OS

TCP/IP Comm. Software
TCP/IP Comm. Software
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TCP/IP and Internet

• 1957 USSR sputnik, USA established ARPA
• 1969 ARPA funded ARPANET
• 1971 Network with 15 nodes
• 1974 Cerf/Kahn Protocol
• 1973 Ethernet (Ph.D Dissertation Bob Metcalfe)
• 1982/83 TCP/IP as a core protocol
• 1983 4.2 BSD Unix with TCP/IP from UCB (univ. of
  California _at_ Berkley)

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TCP/IP Standards
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Internet Technical Bodies

• ISOC - Internet Society. Professional society to
  promote the use of Internet for research and
  scholar communication and collaboration
• IAB - Internet Architecture Board. Technical
  oversight and coordination, falls under ISOC
• IETF - Internet Engineering Task force. Current
  protocols and specifications for standardization.
  Meets 3 times a year, organized in working groups
• IRTF - Internet Research Task force. Research
  oriented for future.

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Internet Administrations

• DDN - the USA Defense Data Network is the
  government organization that has overall
  responsibilty for administrating the Internet
• DDN NIC (Network Information Center)
• assigns unique names and addresses
• collects and distributes information about TCP/IP
  protocols
• IANA Internet Assigned Numbers Authority
• assigns value for network parameters, name of
  services, identifiers
• NOC (Network Operations Center)
• manages communication links

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Internet Standards
Circulated technical documents call Request For
Comments
RFC
Internet Draft
Revision RFC
protocol specifications should be stable
technically and should have no bugs or holes.
Proposed Standard
at least 2 independent and interoperable
implementations that test all specification
funcions
Draft Standard
have had significant field use and clear
community interest in production use.
Official Standard
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Protocol Status Levels

• TCP/IP protocols have one of the following five
  status levels
• Required
• Recommended
• Elective
• Limited use
• Not recommended

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Internet documents

• RFC
• number with RFC XXXX, more than 1700 now
• updated RFCs are published with new RFC numbers
• not all RFCs describe protocols. not all RFCs are
  used
• ftp//ds.internic.net
• STD (STandDard)
• official Internet standard
• FYI (For Your Information)
• RFC series that do not contain protocol
  specifications

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Sample Documents

• RFC
• 2030 I D. Mills, "Simple Network Time Protocol
  (SNTP) Version 4 for IPv4, IPv6 and OSI",
  10/30/1996. (Pages18) (Format.txt) (Obsoletes
  RFC1769)
• 1879 I B. Manning, "Class A Subnet Experiment
  Results and Recommendations", 01/15/1996.
  (Pages6) (Format.txt)
• FYI
• 0023 Guide to Network Resource Tool. EARN Staff.
  March 1994. (FormatTXT235112 bytes) (Also
  RFC1580)
• 0028 Netiquette Guidelines. S. Hambridge. October
  1995. (Format TXT46185 bytes) (Also RFC1855)

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Wireless LANs
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Wireless LANs

• Why RF?
• IEEE 802.11 activities
• RF Technologies - 2.4GHz/5GHz
• Wireless LAN Topology Basics
• Customers WLAN requirements
• Building-to-Building Bridges

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IEEE802.11
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IEEE 802.11
The IEEE 802.11 standard defines the protocol for
two types of networks Ad-hoc and client/server
networks. An Ad-hoc network is a simple network
where communications are established between
multiple stations in a given coverage
area without the use of an access point or
server. The standard specifies the etiquette that
each station must observe so that they all have
fair access to the wireless media. It provides
methods for arbitrating requests to use the media
to ensure that throughput is maximized for all of
the users in the base service set.
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IEEE802.11
The IEEE802 standards committee formed the 802.11
Wireless Local Area Networks Standards Working
Group in 1990. The 802.11-working group took on
the task of developing a global standard for
radio equipment and networks operating in the
2.4GHz unlicensed frequency band for data rates
of 1 and 2Mbps. The standard does not specify
technology or implementation but simply
specifications for the physical layer and Media
Access Control (MAC) layer. The standard allows
for manufacturers of wireless LAN radio equipment
to build interoperable network equipment.
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IEEE802.11
The membership of the committee consists of
individuals from a number of companies and
universities, who research, manufacture, install
and use products in wireless LAN network
applications. Manufacturers of semiconductors,
computers, radio equipment, WLAN systems solution
providers, University research labs and end-users
make up the core group. Companies globally
represent the working group from the United
States, Canada, Europe, Israel and the Pacific
Rim.
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IEEE 802.11 Standard Activities

• 802.11a - 5GHz- Ratified in 1999
• 802.11b - 11Mb 2.4GHz- ratified in 1999
• 802.11d - Additional regulatory domains
• 802.11e - Quality of Service
• 802.11f - Inter-Access Point Protocol (IAPP)
• 802.11g - Higher Datarate (gt20mBps) 2.4GHz
• 802.11h - Dynamic Frequency Selection and
  Transmit Power Control mechanisms
• 802.11i - Authentication and security

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IEEE802.11
Physical Layer Implementation Choices The
Physical Layer in any network defines the
modulation and signaling characteristics for the
transmission of data. At the physical layer, two
RF transmission methods and one infrared are
defined. Operation of the WLAN in unlicensed RF
bands requires the of spread spectrum modulation
to meet the requirements for operation in most
countries. The RF transmission techniques in the
standard are Frequency Hopping (FH) and Direct
Sequence (DS) spread spectrum.
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IEEE802.11
Both architectures are defined for operation in
the 2.4GHz (ISM) frequency band. Each occupies
83Mhz of bandwidth ranging from 2.400 GHz to
2.483 GHz. Differential BPSK (DBPSK) and DQPSK
is the modulation for the direct
sequence. Frequency hopping uses 2-4 level
Gaussian FSK as the modulation signaling method.
The radiated RF power at the antenna is set by
the rules governed by FCC part 15 for operation
in the United States. Antenna gain is also
limited to 6 dBi maximum.
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Range of a Radio Link

• The range of a RF radio link can be calculated by
  using the following items
• Transmitter power
• Receiver sensitivity (at a given data rate)
• Path loss in free space (increases as
  Frequency increases)
• Antenna system gain (includes cable
  losses)

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IEEE802.11
Operating Frequency
Ranges Lower Limit Upper Limit Regulatory
Range Geography 2.402 GHz 2.480 GHz
2.400-2.4835 GHz North America 2.402 GHz
2.480 GHz 2.400-2.4835 GHz Europe 2.473 GHz
2.495 GHz 2.471-2.497 GHz Japan 2.447 GHz
2.473 GHz 2.445-2.475 GHz Spain 2.448
GHz 2.482 GHz 2.4465-2.4835 GHz France

The radiated power is limited to 1W for the
United States, 10mW per 1Mhz in Europe and 10mW
for Japan. There are different frequencies
approved for use in Japan, United States and
Europe and any WLAN product must meet the
requirements for the country in which it is sold.
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IEEE802.11
The MAC Layer The MAC layer specification for
802.11 has similarities to the 802.3 Ethernet
wired line standard. The protocol for 802.11 uses
a protocol scheme know as carrier-sense, multiple
access, collision avoidance (CSMA/CA). This
protocol avoids collisions instead of detecting a
collision like the algorithm used in 802.3. It is
difficult to detect collisions in a RF
transmission network and it is for this reason
that collision avoidance is used. The MAC layer
operates together with the physical layer by
sampling the energy over the medium transmitting
data.
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IEEE802.11
The physical layer uses a clear channel
assessment (CCA) algorithm to determine if the
channel is clear. This is accomplished by
measuring the RF energy at the antenna and
determining the strength of the received signal.
This measured signal is commonly known as RSSI.
If the received signal strength is below a
specified threshold the channel is declared clear
and the MAC layer is given the clear channel
status for data transmission. If the RF energy is
above the threshold, data transmissions are
deferred in accordance with the protocol rules.
The standard provides another option for CCA that
can be alone or with the RSSI measurement.
Carrier sense can be used to determine if the
channel is available.
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IEEE802.11
70
Comparing Radio specs5Ghz vs. 2.4GHz
2.4Ghz (Cisco 350) 5Ghz (802.11a)
TX Power 20dBm (11Mbps) (100mW) 12dBm (6Mbps) (16mW)
RX Sens. -85dBm (11Mbps) -79dBm (6Mbps)
Results 14dBm less for 5Ghz than 2.4 _at_similar
rates. 14dB less gt 50 range reduction
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5GHz vs.. 2.4GHz
2.4GHz Range

• Range of 5GHz is MUCH MUCH less. About 30.
• Overall investment of infrastructure is much
  higher (more APs)

4
5
1
2
3
7
6
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Shared Local Area Network (LAN)
Server
Ethernet
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Wireless Local Area Network (WLAN)
Server
Ethernet
Access Point
Remember An Access Point is a SHARED device and
has similar performance to a SHARED Ethernet HUB.
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Typical Single Cell Configuration
Wireless Cell
LANBackbone
WirelessClients
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Typical Multi-cell Configuration
Channel 1
Channel 6
LAN Backbone
Wireless Cell
Wireless Cell
Access Point
WirelessClients
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Typical Multi-cell Configuration
Channel 1
Channel 6
LAN Backbone
Wireless Cell
Wireless Cell
Access Point
WirelessClients
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Wireless Repeater
Channel 1
Wireless Repeater Cell
LAN Backbone
Channel 1
AccessPoint
WirelessClients
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Standard Office Application

• Use three non-overlapping channels
• Rotate channels to fill in

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• Reduce Cell size
• Reduce Antenna gain or Transmitter power to
  create smaller cell size
• Enable Load Balancing

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Mixed Antenna Example
Maximum Coverage Autorate Negotiation
Wireless for Students DiPole Indoor, Patch Outdoor
Channel 1
Channel 11
Channel 6
Class 1
Class 3
Class 4
Class 2
850
Hallway
Class 8
Class 10
Class 11
Class 9
Channel 1
Channel 11
Channel 6
Building
Courtyard
1000
1000
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END Class 2